Add additional smtp server (for sending only) in Outlook 2011 Mac Issue

A user has setup an IMAP account  (*** Email address is removed for privacy ***) and can send email out in office LAN that don't need smtp authentication.

When he works out of office that using mobile phone network, sending email needs smtp authentication for his company email server.

So he wants to setup two account with same email address.

1. Name: IMAP account - IMAP account (*** Email address is removed for privacy ***) 

2. Name: ms (outside) - POP account (*** Email address is removed for privacy ***) and leave mail on server, SMTP needs authentication.  (for sending email only)

When he works out of office, he will choose "ms (outside)" account to send out email.

Probem is here. It will download all emails from POP account if check emails.  Though set schedule that don't check for  "ms (outside) - POP account", it still download all emails.

How to setup that only IMAP account check email only? The other POP account is just for SMTP Server.

Thanks.